Such a transcoder unit is known from EP 600 197 A2. There, a transcoder unit for a wireless telecommunications network, namely for a mobile radio network, is described. It contains several arithmetic units in the form of digital signal processors for performing transcoding operations on voice signals which are digitally transmitted on several communication channels. Use is made of transcoding methods which are specified in the GSM (Global System for Mobile Communications) standard. According to the description in column 2, lines 4 to 52, of that reference, five processors support the transcoding of eight communication channels. As also described there, the transcoder unit includes an input/output processor which controls access to the individual signal processors. These measures reduce the number of signal processors required. All processors used, i.e., all arithmetic units, are disposed on a circuit board. Transmission of digital voice signals at different transcoding rates is not described there.
In a mobile radio network based on the GSM standard, transmission modes with different transcoding rates are provided. Recommendations GSM08.60, GSM06.10-12, and GSM06.31-32 define the so-called full rate mode, in which voice signals are transcoded between transmissions at 16 kb/s and 64 kb/s. GSM08.61, GSM06.20-22, and GSM06.41-42 define the so-called half rate mode, in which voice signals are transcoded between transmission at 8 kb/s and 64 kb/s. GSM08.60, GSM60-62, and GSM6.81-82 define the so-called enhanced full rate mode, which corresponds to an improvement on the full rate mode in terms of signal quality. The construction of a transcoder unit is not dealt with in the GSM standard.